Material for cold rolled stainless steel and container made thereof

ABSTRACT

A material for cold rolled stainless steel has a chemical composition comprising: C: 0.08% or less, Si: 0.9% or less, Mn: 2% or less, P: 0.045% or less, S: 0.03% or less, Ni: 8% to 10.5%, Cr: 17.5% to 20%, Cu: 0.3% to 2.1%, and the balance of substantially Fe, wherein the cold rolled stainless steel has a tensile strength of 515 N/mm2 or more, a yield strength of 205 N/mm2 or more, and an elongation of 40% or more.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention generally relates to a material for cold rolled stainless steel and, more particularly, to a material for cold rolled stainless steel suitable in microwave source without producing arcing problem.

2. Description of the Related Art

Microwave heating devices such as microwave ovens are one of the essential kitchen equipment nowadays. Microwave ovens can be used for reheat foods quickly and easily. Therefore, it is convenient to get hot foods at any time.

However, generally, metal products known in the prior art cannot be used in microwave ovens. The energy produced by microwave ovens generates a high electric field on the metal products and leads to arcing phenomena. Once the arc has been excited in an air ionized by one or more sparks, the arc absorbs a very high quantity of energy, resulting in serious damage of the metal products. In order to avoid the danger, the microwavable food containers are limited to made of non-metallic material. Therefore, how to provide a metal material which can be used in microwave heating devices without producing sparks has become an urgent problem to be solved in the industry.

SUMMARY OF THE INVENTION

In light of solving the foregoing problems of the prior art, in the first aspect, the present invention provides a material for cold rolled stainless steel suitable for using in microwave heating devices without producing sparks. The material for cold rolled stainless steel according to the present invention has a chemical composition comprising, by mass %, C: 0.08% or less, Si: 0.9% or less, Mn: 2% or less, P: 0.045% or less, S: 0.03% or less, Ni: 8% to 10.5%, Cr: 17.5% to 20%, Cu: 0.3% to 2.1%, and the balance being substantially Fe, wherein the cold rolled stainless steel has a tensile strength of 515 N/mm² or more, a yield strength of 205 N/mm² or more, and an elongation of 40% or more.

In an embodiment, the material for cold rolled stainless steel of the present invention has a chemical composition consisting of, by mass %, C: 0.08% or less, Si: 0.9% or less, Mn: 2% or less, P: 0.045% or less, S: 0.03% or less, Ni: 8% to 10.5%, Cr: 17.5% to 20%, Cu: 0.3% to 2.1%, Mo: 0.2% or less, V: 0.2% or less, and a balance of Fe, wherein the cold rolled stainless steel has a tensile strength of 515 N/mm² or more, a yield strength of 205 N/mm² or more, and an elongation of 40% or more.

In an embodiment, the chemical composition contains, by mass %, 0.04% to 0.06% of C.

In an embodiment, the chemical composition contains, by mass %, 0.4% to 0.6% of Si.

In an embodiment, the chemical composition contains, by mass %, 1% to 1.5% of Mn.

In an embodiment, the chemical composition contains, by mass %, 0.02% to 0.04% of P.

In an embodiment, the chemical composition contains, by mass %, 0.002% to 0.005% of S.

In an embodiment, the chemical composition contains, by mass %, 8% to 8.5% of Ni.

In an embodiment, the chemical composition contains, by mass %, 18% to 18.5% of Cr.

In an embodiment, the chemical composition further comprises Mo or V, wherein the content of Mo or V is 0.2% or less.

In the second aspect, the present invention provides a container. The container is made of a material for cold rolled stainless steel described in the first aspect of the present invention.

Compared to the prior art, the material for cold rolled stainless steel of the present invention do not create the electric arcs or sparks in microwave heating devices. Therefore, the metallic material of the present invention can be made into microwavable food containers.

DETAILED DESCRIPTION

The present invention is described by the following specific embodiments. Those with ordinary skills in the arts can readily understand other advantages and functions of the present invention after reading the disclosure of this specification. Any changes or adjustments made to their relative relationships, without modifying the substantial technical contents, are also to be construed as within the range implementable by the present invention.

Hereinafter, the unit “%” or “% (m/m)” relating to the content of elements in the chemical composition refers to “mass %”, which is mass percentage unless specified otherwise.

A material for cold rolled stainless steel provided by the first aspect of the present invention has the chemical composition comprising, by mass %, C: 0.08% or less, Si: 0.9% or less, Mn: 2% or less, P: 0.045% or less, S: 0.03% or less, Ni: 8% to 10.5%, Cr: 17.5% to 20%, Cu: 0.3% to 2.1%, and a balance of Fe. According to the standard GB/T 228.1-2010, the material has a tensile strength of 515 N/mm² or more, a yield strength of 205 N/mm² or more, and an elongation of 40% or more.

In an embodiment, the material for cold rolled stainless steel of the present invention has the chemical composition consisting of, by mass %, C: 0.08% or less, Si: 0.9% or less, Mn: 2% or less, P: 0.045% or less, S: 0.03% or less, Ni: 8% to 10.5%, Cr: 17.5% to 20%, Cu: 0.3% to 2.1%, Mo: 0.2% or less, V: 0.2% or less, and a balance of Fe. According to the standard GB/T 228.1-2010, the material has a tensile strength of 515 N/mm² or more, a yield strength of 205 N/mm² or more, and an elongation of 40% or more. In this embodiment, the stainless steel alloys of the present invention is described in a closed-end content by using the term “consisting of” to reveal the chemical elements in various percentages. However, those with ordinary skills in the arts should understand that the material of stainless steel can have other trace elements, such as Al, Nb, Ti, W or B, wherein the content of the trace elements is about 0.01% or less than 0.01%, or the material of stainless steel can have unavoidable chemical elements present in the stainless steel alloys because of the limitation of manufacturing technology or cost, and the content of unavoidable elements is limited to 0.01%.

In an embodiment, the content of C of the material for cold rolled stainless steel is 0.04% to 0.06%.

In an embodiment, the content of Si of the material for cold rolled stainless steel is 0.4% to 0.6%.

In an embodiment, the content of Mn of the material for cold rolled stainless steel is 1% to 1.5%.

In an embodiment, the content of P of the material for cold rolled stainless steel is 0.02% to 0.04%.

In an embodiment, the content of S of the material for cold rolled stainless steel is 0.002% to 0.005%.

In an embodiment, the content of Ni of the material for cold rolled stainless steel is 8% to 8.5%.

In an embodiment, the content of Cr of the material for cold rolled stainless steel is 18% to 18.5%.

Please refer to Table 1 below. It shows each chemical composition by mass % contained in Examples 1 to 5 and Comparative Examples 1 to 3.

Preferred ranges of each chemical composition included in the material for cold rolled stainless steel provided by the present invention were shown in Examples 1 to 5. These materials for cold rolled stainless steel of the present invention may have the tensile strength between 635 and 670 N/mm², the yield strength of about 270 N/mm² and the elongation of about 60% according to the present invention. These materials for cold rolled stainless steel of the present invention may have hardness between 165 and 175 HV measured by following the standard GB/T4340.1-2009.

In the present invention, the content of Si of the material for cold rolled stainless steel being 0.9% or less than 0.9% is the most critical for the microwavable properties of the material. According to the present invention, the stainless steel of the Comparative Example 1 with higher content of Si may have a higher risk of sparking when it is heated by microwave. Therefore, according to the present invention, the materials for cold rolled stainless steel of the Examples 1 to 5 are more suitable for being used in microwave heating devices.

The material of stainless steel provided by Comparative Example 2 containing less than 0.9% of Si significantly reduced the chance of sparking in the microwave source. However, its Cu content is more than 2.1% so Comparative Example 2 would be affected by microwave and the safety cannot be ensured every time when being used.

TABLE 1 Stainless steel Chemical composition (mass %, the balance being substantially Fe) No. C Si Mn P S Ni Cr Cu Example 1 0.044 0.53 1.311 0.03 0.004 8.006 18.089 0.56 Example 2 0.041 0.417 1.301 0.03 0.003 8.025 18.153 1.32 Example 3 0.048 0.437 1.352 0.026 0.005 8.023 18.056 1.947 Example 4 0.046 0.488 1.182 0.04 0.003 8.071 18.12 0.392 Example 5 0.056 0.421 1.071 0.03 0.002 8.024 18.199 1.541 Comparative 0.047 0.98 1.243 0.031 0.003 8.03 18.123 0.85 Example 1 Comparative 0.026 0.615 1.264 0.032 0.005 7.87 17.93 2.153 Example 2 Comparative 0.049 0.481 1.36 0.038 0.003 8.37 16.787 0.335 Example 3

In an embodiment, in addition to the chemical composition shown in Table 1, the material for cold rolled stainless steel of the present invention further comprises Mo or V. The content of Mo or V may be 0.2% or less. In a preferred embodiment, the content of Mo or V is about 0.1%.

In an embodiment, the material of the stainless steel of the present invention further comprises other trace elements, such as Al, Nb, Ti, W or B, but not limited thereto. The content of the trace elements is about 0.01% or less than 0.01%.

In an embodiment, the material of the stainless steel further comprises unavoidable substances, i.e. impurities, such as Mg, P, S, Al, Nb, Ti, W or B, but not limited thereto. The unavoidable substances are present in the stainless steel alloys because of the limitation of manufacturing technology or cost. The content of impurities is limited to 0.01%.

The Microwave Suitability Test (Standard EN 15284: 2007)

In the TUV test report (No. TUV SZ 168281464 HHQ01), the test for microwave suitability is carried out by the standard EN 15284: 2007. The sample of the stainless steel is placed in a microwave oven for 10 minutes at 1000 W. After the sample was cooling, there are some requirements, such as cracking, crazing, color change and sparking, need to be checked. The test is repeated 3 times and there is no visual changes on the sample made of the material for cold rolled stainless steel provided by the present invention after each microwave cycle.

The Microwave Safety Test

According to the SGS test report (No. T32020300394SN), the samples made of the material for cold rolled stainless steel provided by the present invention have undergone a 10-minute test with IEC 1700 W for 3 cycles. Then, the samples are visually examined whether the samples show any sign of damage by comparison the sample of control group which is not exposed to microwave. According to the present invention, the test result shows that the appearance of the samples made of the material for cold rolled stainless steel provided by the present invention have no noticeable changes after microwave cycles.

In the present invention, the content of Cr may be 17.5% to 20%. Higher Cr content may increase the antirust ability for the stainless steel. According to Comparative Example 3, its Cr content is less than 17.5%. Although its Si content is less than 0.9% and its Cu content is between 0.3% and 2.1%, the material has the poorer antirust ability and is not suitable for being used in food containers.

The material for cold rolled stainless steel of the present invention comprises the balance being substantially Fe, which means that the remaining amount of the material of the stainless steel would be iron. Therefore, the remaining amount of Fe can be different in the above embodiments.

In the second aspect, the present invention provides a container. The container is made of a material for cold rolled stainless steel described in the first aspect of the present invention.

According to the present invention, the material of cold rolled stainless steel of Examples 1 to 5 can be the preferred embodiments for producing the container of the present invention.

In summary, the material for cold rolled stainless steel of the present invention overcomes the problem that the metal products generate the electric arcs and sparks in microwave heating devices in the prior art. The material is tested by the certification authority SGS and TUV. Both of the test reports show that using and heating the container made of the material for cold rolled stainless steel of the present invention in microwave ovens is pretty safe. Therefore, the material for cold rolled stainless steel of the present invention can be used to make a container used for microwave heating without causing the damage to the container or microwave ovens.

The foregoing descriptions of the detailed embodiments are only illustrated to disclose the features and functions of the present invention and not restrictive of the scope of the present invention. It should be understood to those in the art that all modifications and variations according to the spirit and principle in the disclosure of the present invention should fall within the scope of the appended claims. 

1. A material for cold rolled stainless steel comprising a chemical composition containing, by mass % (m/m): C: 0.08% or less, Si: 0.9% or less, Mn: 1% to 1.5%, P: 0.045% or less, S: 0.03% or less, Ni: 8% to 10.5%, Cr: 17.5% to 20%, Cu: 0.3% to 2.1%, and the balance being Fe, wherein the content of Fe is 65% to 74%, wherein the cold rolled stainless steel has a tensile strength of 515 N/mm² or more, a yield strength of 205 N/mm² or more, and an elongation of 40% or more.
 2. The material for cold rolled stainless steel of claim 1, wherein the content of C is 0.04% to 0.06%.
 3. The material for cold rolled stainless steel of claim 1, wherein the content of Si is 0.4% to 0.6%.
 4. (canceled)
 5. The material for cold rolled stainless steel of claim 1, wherein the content of P is 0.02% to 0.04%.
 6. The material for cold rolled stainless steel of claim 1, wherein the content of S is 0.002% to 0.005%.
 7. The material for cold rolled stainless steel of claim 1, wherein the content of Ni is 8% to 8.5%.
 8. The material for cold rolled stainless steel of claim 1, wherein the content of Cr is 18% to 18.5% of Cr.
 9. The material for cold rolled stainless steel of claim 1, the chemical composition further comprises Mo or V, wherein the content of Mo or V is 0.2% or less, by mass % (m/m).
 10. A container, made of the material for cold rolled stainless steel of claim
 1. 